1. Field of the Invention
The present invention relates to a device for draining a paper machine felt, and in particular, from an interior side of a circulating felt belt, via centrifugal force at a region of convex curvature of the felt interior side. A paper machine felt of this type is an endless felt belt that supports a fibrous pulp sheet in a press section of a paper machine and that absorbs fluid or moisture from the fibrous pulp sheet in the press zone.
2. Discussion of Background Information
Outside the press zone, felts similar to the one generally described above, tend to transfer water back to the fibrous pulp sheet, which results in an undesirable re-moistening of the fibrous pulp sheet.
Known paper machine felts are constructed in a double-sided manner having a dense, fibrous web on a paper side and a coarse support side with void spaces and openings, e.g., a synthetic material screen, on the opposite (interior) side. With this felt construction, water may be spun off at high speeds in a centrifugal force field. The felt may be guided into this centrifugal force field by placing the coarse interior side on a convex track. The water to be spun off is stored in the void spaces, and is caught in a catch trough located in the interior of the felt loop. The spin off process only starts at a velocity in which the centrifugal force surpasses the felt's ability to retain the water, which is based upon surface tension forces.
Even if the fiber web is manufactured with such high density that air cannot easily pass therethrough, pre-conditions for water spin-off are still not met because no air can pass between the fiber web and the water layer. Protruding water, which sucks water from the web mesh due to surface tension and initiates a convection movement, develops slowly on the surface and results in an exchange of water and air in the support layer of the felt. Due to shortness of most interior convex looping zones in the run direction of a paper machine felt and due to an initial time delay during which the convection effect is produced, only a limited amount of water can be spun off.